Propane dewaxing of lubricating oils



May 15, 1956 w. TQ KNOX, JR 2,745,791

PROPANE DEWAXING OF' LUBRICATING OILS Filed June 19, 1953 HVL()4 @Ijvegg l 3 ATTORNEY United States Pater PRoPANE DEWAXING or LUBRreArmoons William T. Knox, Ir., Cranford, N. E., assigner to Esso Research andEngineering Company, a corporation of Delaware Application June 19,1953, Serial No. 362,735

2 Claims. (Cl. 196-13) The present invention is generally concerned withthe solvent dewaxing of petroleum oil fractions. The invention is moreparticularly concerned with an improved process for the dewaxing oflubricating oil fractions with a light hydrocarbon solvent, as forexample a solvent comprising propane. process .undesirable ice formationis prevented in a solvent. dewaxing operation utilizing a solvent suchas propane, by employing in'conjunction with the propane a relativelysmall amount or" ammonia.

ln the refining of hydrocarbon oils such as petroleum oils, it is knownto segregate waxes from so-called parafn distillates, waxy lubes and thelike. The segregation of these waxes is secured by a number ofprocesses. For example, it is known to chill the selected wax containingfraction in order to secure crystallization of the wax and to remove thewax crystals from the oil by filtering, centrifuging and the like. It isalso known to use various dewaxing solvents such as liquid normallygaseous hydrocarbons, such as propane, as well as other solvents, suchas methylethyl ketone and the like. It is also known to utilize indewaxing operations solvent mixtures wherein one solvent comprises a waxprecipitating solvent while the other comprises a solvent having a highsolubility for oil. A solvent mixture of this character, for example,comprises 40% by volume of l toluene and 60% by volume of methylethylketone.

When utilizing a solvent such as propane in a dewaxing operation whereinthe stock being treated is subjected to low temperatures, the waterpresent freezes with the resultant plugging of ow lines, valves, sprays,compressor elements and the like. At times the ice freezes insufficiently large pieces to actually rend the iilter cloth. Otherdisadvantages result due to ice crystals in the system. For instance thepresence of ice aiects the wax crystallization erratically, resulting inpoor filtration rates. The ice crystals may also impregnato the ltercloth giving progressive blinding of the cloth. Furthermore, the icingof instrument lines presents a very real problem since the effectivenessof the operation is controlled by effectively operating instruments. Theicing causes these instruments to give poor control to the entiredewaxing operation. In many instances it has been necessary to shut downthe plant in order to allow the equipment to be heated so as to melt theic This water enters the system by various paths. It may be present inthe feed oil or in the overhead from the steam stripper. Furthermore,since the ice will remain with the wax on the filter cloth, solventrecovered from the wax is segregated as wet solvent. Only the drysolvent recovered from the filtrate can be chilled and used in the heatexchangers. The solvent of course can be dried out but this operation isrelatively expensive.

ln accordance with the present invention an improved dewaxing process issecured by utilizing in conjunction v with the dewaxing solvent anamount of ammonia, less than about 2% by weight preferably less than 1%by ln accordance with the present A weight based upon the total quantityof solvent utilized. r`he use of ammonia as a freezing point depressantis unique because no other additive can be used which will be eective insuch small amounts, and whichn also can be completely used up. Anyexcess of the ammonia will be recycled with the solvent. A particularlydesirable feature is that ammonia has essentially the same vaporpressure-temperature curve as propane. Therefore, an excess of ammoniamay be added and will simply follow the propane through the ash andstripping units.

The process of the present invention may be more fully understood byreference to the drawing illustrating one embodimentof the same.

A waxy feed which comprises a waxy distillate boiling in the lubricatingoil boiling range is introduced into the system by means of line 1. Inaccordance with the present invention a quantity of propane (1 4 volumesof propane per volume of oil) is mixed with the waxy feed by means ofline 2. Also, in accordance with the present invention this propane willcontain less than 2%, preferably less than 1% of ammonia which isintroduced by means of line 3.

The mixture is passed through a heating zone 4 wherein the mixture israised to a temperature in the range from about 140 F. to 180 F. tosecure complete miscibility. The mixture is passed to a cooler 5 in heatexchange 'with a cooling iiuid which is passed countercurrently asillustrated diagrammatically by 6. The cooled mixture is passed intochilling zones 7 and 8 operated alternately. When it is desired toby-pass vchilling zone '7 feed line 9 is used.

Por the purpose of description, assume that zone 7 is being chilledwhile zone S is being pumped out and the product filtered. Chilling inzone 7 is secured by vaporizing the propane which is removed overhead bymeans of line it), compressed in compressor 11 and condensed in coolingzone 12. The condensed propane is recycled by means of line 2. Thechilled product at a temperature in the range from about 30 F. to 40 F.is removed from chilling zone 7 by means of line 16 and introduced intoa conventional rotary type drum filter This unit comprises a rotary drumcontaining thereon a iilter cloth the lower half of which is submergedin a. mass of chilled slurry. The wax collects on the periphery of thedrum as it rotates while the ltrate passes through the filter cloth andis removed from the center of the drum by means of line i8. ln normaloperation ice collects with the wax on the lter cloth. As the drumrotates it is preferably washed with propane through spray element 19supplied by means of line 20. This washed propane may be removed by aseparate line 2i and used as desired.

rhe wax is removed from the drum with the aid of a scraper element 22and blowback gas and introduced into a solvent removal zone Z3, by meansof line 5i). Solvent and water are removed overhead from zone 23 bymeans of line 24 while a solvent-free wax fraction is removed by meansof line 25. rThe lube oil fraction removed by means of line 1S is passedto a distillation zone which comprises two or more distillation stages26 and Z7. Temperature and pressure conditions in zone 25 are adapted toremove overhead by means of line 28 most of the solvent. This iscondensed in condenser 29 and recycled in the system. Zone 26 isoperated at a pressure in the range from about 175 to 225 lbs. per sqin. gauge. The lubricating oil containing a small amount of propane isremoved from zone 26 by means of line 3i? and introduced into anatmospheric distillation or stripping zone 27. The nal traces of propaneare removed from the dewaxed oil by stripping steam which is introducedby means of line 31. The dewaxed oil free of' solvent is removed bymeans of line 32 while Wet propane is removed overhead by means of line33; The overhead stream is passed through cooler 34 and then into aseparation Zone 51. The condensed water is removed by means of line 52while the vap'orous propane is compressed by means` of compressor 74 andcondensed by means of cooler 53. This stream is recycled to the system.

As pointed out heretofore, water present tends to clog up the filtercloth, transfer lines, the spray equipment and the compressors; However,.in accordance with the present invention the added ammonia causes thewater to form a` lower liquid ammoniacal water phase during'the chillingcycle. kThis phase is withdrawn from chiller 7 by means of line 35 andfrom chiller 8 by means of line 36.

The overhead from zone 23 comprising propane, water and ammonia ispassed through cooler 61 and introduced into a settler 42. Propane andammonia are removed overhead from settler 42 by means of line 63, passedthrough' a compressor 45, a cooler 41 and recycled to the system. Anammonia-water phase is removed from the bottom of settler 42 by line 40and combined with the water and ammonia removed from chillers 7 and 8 bylines 35 and 36. An ammonia-water phase is also removed from the bottomof settler 51 by means of line 52 and combined with the ammonia-waterphases from settler 42 and Chillers 7 and 8. This combined stream ispassed to distillation zone 37 by' means of line 38. Temperature andpressure conditions in zone 37 are adapted to remove overhead by meansof line 43 ammonia which is recycled to the system by means'of line 3. Awater phase is removedl from the bottom of zone 37 by means of line 44.

Thus, by the present process all water is removed in the chilling zoneas a liquid ammoniacal water phase which prevents any diiculties due'to' icing during the latter stages of the process.

When 1% of ammonia is presentr in propane, equilibrium data show thatthe water phase lwill contain about 22% of ammonia. This liquidammoniaca] water phase has a freezing point yof 40 F. which is belownormal dewaxing temperatures. Since the amount of water present is verysmall compared with the amount of propane, the ammonia concentration inpropane is maintained only slightly higher than equilibriumconcentrations.

What is claimed is:

l. In the propane'Y dewaxing of waxy hydrocarbon distillate in thepresence of water, the improvement of inhibiting ice formation by saidwater comprising the steps of adding to a mixture of said waxyhydrocarbon distillate and propane a freezing point depressantconsisting essentially of yamrno'niafin the amount lof less than about2% by weight based on' the amount of propane present, chilling themixture s'o' formed to' a temperature in the range of fromv about l`30lF. `to 40 F., whereby a separate immiscible ammoniacal water phase isformed, separating said immiscible'phase from the chilledwa'xLdistillatelpropane mixture, and subsequently filtering said chilledmixture to recover precipitated wax.

2. The process according to'claim" 1` wherein'the amount of ammonia usedis inV the range4 of from about 0.2 to 1% by Weight.

References Cited inthe filer' ofA thisv patent,Y UNrTEn STATES PATENTS2,067,128 Manley f. Jan. 5, `1937 2,096,725 Andrews et a1. ocnza, 19372,478,456 Boudreaux et al. Aug; 9, 1949

1. IN THE PROPANE DEWAXING OF WAXY HYDROCARBON DISTILLATE IN THEPRESENCE OF WATER, THE IMPROVEMENT OF INHIBITING ICE FORMATION BY SAIDWATER COMPRISING THE STEPS OF ADDING TO A MIXTURE OF SAID WAXYHYDROCARBON DISTILLATE AND PROPANE A FREEZING POINT DEPRESSANTCONSISTING ESSENTIALLY OF AMMONIA IN THE AMOUNT OF LESS THAN ABOUT 2% BYWEIGHT BASED ON THE AMOUNT OF PROPANE PRESENT, CHILLING THE MIXTURE SOFORMED TO A TEMPERATURE IN THE RANGE OF FROM ABOUT +30* F. TO -40* F.,WHEREBY A SEPARATE IMMISCIBLE AMMONIACAL WATER PHASE IS FORMED,SEPARATING SAID IMMISCIBLE PHASE FROM THE CHILLED WAX-DISTILLATE-PROPANEMIXTURE, AND SUBSEQUENTLY FILTERING SAID CHILLED MIXTURE TO RECOVERPRECIPITATED WAX.